1. Field of the Invention
The world's supply of oil, natural gas, coal, and uranium are becoming depleted due to exponential growth in population and the need for every greater amounts of energy to satisfy the resulting economic growth. Furthermore, the pollution from the widespread use of these fuels has caused tremendous concern over the possibility of catastrophic widespread and irreversible environmental damage, such as, but not limited to, global warming. Clearly there is a limit to growth in a world constrained by finite resources and a finite ability of the environment to absorb the pollution of human activities. To help overcome the limitations of conventional fuels the use of the energy from our sun would appear to offer many advantages, such as its pollution free quality and its pervasive global distribution, if only it could be harvested in a cost effective and efficient way using devices that only require a relatively small investment in energy and pollution for their manufacture. This invention directly addresses the problem of creating an efficient, low-cost, and easily manufacturable solar tracker and collector, thereby providing a means to directly tape the energy resources of the sun by either replacing or augmenting the performance of solar concentrators with a solid-state electro-optic sun tracker that is capable of adapting to changing environmental lighting conditions.
In general, solar concentrators increase the flux of solar energy through a give area. This in turn can be used to maximize the power output of photovoltaic cells, which are significantly and nonlinearly improved in performance when irradiated by intense sunlight. Specially designed solar cells, which are optimized for use in intense sunlight, are capable of producing more output power than a large area of solar cells at a lower concentration due to the increased quantum efficiency of the cells in this intense light environment. Concentrators also provide a means to confine solar energy into a small cross-sectional area light-guide, thereby making solar energy distribution practical for a variety of uses. Unfortunately, solar concentrators have an intrinsically narrow field of view—diminishing with increasing concentration. This necessitates the use of some kind of tracking device to follow the sun's motion.
More specifically, the present invention relates to the field of electronically controllable and adaptable solid-state solar trackers that are based on predominantly flat optical boundaries which refract the sunlight and have a reconfigurable orientation. This optical boundary provides a means to direct light into a desired direction for the purpose of collection, concentration, distribution, and conversion of the sunlight into other end-use energy products.
Furthermore, this invention is less expensive and less resource intensive to manufacture than other solar energy harvesting technologies because it allows solar harvesting to be integrated directly into buildings and other structures without the outward mechanical infrastructure that is typical of conventional solar technologies. That is, it dramatically reduces the balances of systems infrastructure costs. The present invention is solid-state, has a very thin profile allowing it to cover large areas of structures such as, but not limited to, buildings aircraft, satellites, ocean vessels, and solar farming structures. Additionally, this invention allows the use of the best of breed in solar concentrator optics and concentrating solar cells or it can even be used as a stand-alone concentrator technology. Its versatility and adaptability make it an ideal candidate for small-scale domestic solar energy applications or large-scale industrial power-plants.
2. Description of the Prior Art
There are several recent efforts to adapt a twisting ball concept for use in solar energy collection and concentration. Additionally, There are many patents that explicitly show the use of twisting balls, called gyricons, for use in electronic paper and display technology. No other prior art appears to utilize the balls to optically concentrate or focus the sunlight by using a process of refraction within the twisting balls. Furthermore, the prior art neither teaches or anticipates our application of adaptive transmission-mode solar tracking. From the point of view of this patent the more recent prior art patent applications related to solar energy concentration using rotating optical devices are significant, however, they have many disadvantages as are considered in detail below.
The more recent prior art patents are related to using twisting ball technology in a reflection mode only. The prior art of reflection mode twisting ball solar trackers and concentrator has a number of significant disadvantages. In contradistinction, later it will be shown how the advantages of a refraction mode device, can overcome the disadvantages of the prior art.
Both the solar twisting ball concept and the gyricons used in displays are active devices that rotate either a ball or cylinder by use of electric or magnetic fields with the intent of utilizing these rotating structures in either diffuse or specular reflection. Much emphasis has been placed on the use of a quasi-electrostatic drive of the twisting balls and cylinders due to the ability for low power draw. Unfortunately, much of the prior art shows electrostatic motors with high complexity, low precision, and relatively high power dissipation even though the electrostatic motor technology has a longer history than the magnetic induction motor. Indeed, the first simple electrostatic motors were actually developed in the 1750's by Benjamin Franklin and Andrew Gordon. Subsequently, electret based electrostatic motors were invented in 1961 by a Russian physicist, A. N. Gubkin. His motor is based on an electret materials made in 1922 by Mototaro Eguchi, professor of physics at the Higher Naval College in Tokyo. Many different embodiments have evolved since the original principle was reported none of which teaches or anticipates the use of the electrostatic motor for controlling a transmission mode solar tracking device as described in this invention.
The disadvantages listed below apply to many inventions. However, the disadvantages listed below are especially pertinent with regard to the inventions of Mario Rabinowitz et. al. and Toshiro Higuchi et. al., which are explicitly listed later in this document.
The first disadvantage of the prior art is that it mimics the functionality of large curved surface reflectors, such as mirrored parabolic concentrators, which require a mast structure at the focal point to hold the receiver and collect the concentrated solar radiation. This mechanical mast structure adds to the balance of systems costs for the system and is not compatible with compact integrated solar energy collection, concentration, and distribution devices.
The second disadvantage of the prior art is that the mirror technology used is based on thin metallic films which are sandwiched between an upper and lower hemisphere of transparent dielectric. These metallic films are very difficult to manufacture with low ohmic losses. The result is that any practical metallic mirror will typically have losses that can range from about 2% to 20% depending on the process used and the resulting purity of the metal and it's surface roughness. The lower loss mirrors cost significantly more to fabricate, especially when incorporated into very small dielectric balls or cylinders.
A third disadvantage of the prior art is that the metallic mirrors also interact with the switching electric fields to produce ohmic losses via eddy currents. Although the power loss in an individual twisting ball is tinny, the total loss from many millions of twisting balls can be quite large. This reduces the efficiency of the overall solar harvesting process.
A fourth, and extremely significant, disadvantage of the prior art is that the reflection mode operation has an intrinsic shadow loss directly related to the use of a mirror. This is because when an array of twisting balls or cylinders is closely packed, as is the case when collecting and concentrating sunlight, part of the reflected energy from one mirror is reflected onto the backside of an adjacent mirror whenever the solar source is not directly in front of the mirrors, which is almost always the case. That is to say, an array of tilted close-packed mirrors partially shadows itself due to geometric considerations.
A fifth disadvantage of the prior art utilizing reflection mode optics is that it cannot be integrated in intimate contact with other optical devices because the input surface and the output surface are the same. Hence, the inclusion of, for example, an optical output lens directly on top of the reflection mode array would interfere with the input of the light. In contradistinction, a trans-mission mode device would allow direct integration of the twisting ball solar tracker with optical structures, thereby reducing the volume of integrated optics for solar collection, concentration, distribution, and conversion devices.
A sixth disadvantage of the prior art is that it requires significant currents to induce the required electric fields to twist large numbers of balls and embedded mirrors over large distances. The prior art attempts to overcomes this difficulty by periodically resetting the twisting balls in order to track the sun instead of maintaining a control electromagnetic field. However, this requires that the prior art have two modes. The first mode is the dynamic mode where in the twisting balls are moved in accordance with the applied electric fields. The second mode is a mechanical stabilization mode where mechanical forces are applied to hold the twisting balls between dynamic updates. The mechanical stabilization is achieved by one of a number of possible techniques, such as but not limited to, piezo-electrics, fluid pressure, and ancillary electric or magnetic moments that are engaged to produce forces for the stabilization mode. Furthermore, because all the driving electrodes are typically quite far from the moving structures large voltage supplies are required.
A seventh disadvantage of the prior art is that it does not adequately address the problem of pointing accuracy or pointing precision. Pointing accuracy is related to the absolute error in solar tracking and pointing precision is related the relative error in solar tracking. The accuracy and the precision of orientating balls or cylinders, and hence redirecting light, directly impacts the performance of the subsequent solar concentration process due to the limitations imposed by the principle of conservation of etendue—which is based on a phase space approach to light focusing dynamics. The prior art is useful only for the relatively low pointing accuracies needed for concentrations on the order of 10 suns. That is 10 times the normal one sun concentration. In applications that require concentrations that are on the order of 1000 suns, 10,000 suns, or even as high as about 100,000 suns—which is near the thermodynamic limit of concentration in a homogenous, isotropic, and linear dielectric medium—a more robust means of providing the required pointing accuracy and precision is needed. Additionally, a means must exist to overcome the segmented nature of light redirected from a discrete twisting ball. This discrete nature of reflection mode twisting balls and cylinders tends to limit the maximum achievable concentration when arrays of twisting structures attempt to directly focus light to a common focal point directly. Such focusing problems would not exist if the array of twisting mirrors used in the prior art only were used to redirect the input light so that an intermediary high-performance solar concentrator could be used to perform the concentration. The prior art neither teaches or discusses this important issue for high performance solar concentration.
An eighth disadvantage of the prior art, especially with regard to electrostatic motors, is that it shows electrostatic stepping-motor actuation based on three or more phases of interdigitated electrodes on a single stator. An example of this is shown in the prior art of FIG. 5. In principle, only two phases are really needed so long as a means exists to form a perturbation to cause the rotor to be assigned a specific direction of travel.
A ninth disadvantage of the prior art, especially with regard to electrostatic motors, is that it shows electrostatic stepping-motors that do not optimally utilize the electrode geometry. In particular, for a given pitch between electrodes an optimal resolution of travel of only one pitch length should be achievable in theory. The prior art does not achieve this theoretical limit and therefore wastes precious area resources needlessly.
A tenth disadvantage of the prior art, especially with regard to electrostatic motors, is that the multi-phase nature of the electrode voltage distributions necessitates the use of complex geometries to make the electronic connections. Such complexity would reduce the transmission of the light through any optics due to the non-zero absorption of each layer of imperfectly transparent conductors, such as but not limited to, Zinc Tin Oxide (ZTO) and indium Tin Oxide (ITO).
An eleventh disadvantage of the prior art, especially with regard to electrostatic stepping motors, is that it does not integrate optics into the functionality of the stator, rotor, or slider.
A twelfth disadvantage of the prior art in electrostatic stepping motors is that the electrical interconnections of three of more phases of belt-like electrodes requires that the electrical interconnections are distributed on more than one layer of dielectric. This requires complex fabrication and introduces the possibility for electrical cross talk in an environment of high voltages that are typical in electrostatic motor design.
It also appears that none of the prior art associated with display technology utilizes twisting balls or cylinders to optically concentrate, or focus, light using transmission mode, also called refraction mode, optics, as is done in this present invention. Furthermore, the prior art neither teaches nor anticipates the use of twisting ball or cylinder technology for solar energy conversion applications. Furthermore, the prior art neither teaches or anticipates the use of twisting ball or cylinder technology as a means to functionally separate solar energy harvesting into four distinct steps: collection, concentration, distribution, and energy conversion.
The following are a list of the issued patents that use twisting ball or cylinder technology (gyricons) explicitly for solar concentration. These patents clearly do not anticipate, or show in any way, the use of a refraction mode twisting balls and twisting cylinders for solar tracking and concentration.
U.S. Pat. No. 6,612,705 issued to Mark Davidson and Mario Rabinowitz on Sep. 2, 2003 deals with reflection mode mini-optic twisting balls and twisting cylinders that use metallic mirrors for reflection and electric and magnetic addressing.
U.S. Pat. No. 6,698,693 issued to Mark P. Davidson and Mario Rabinowitz on Mar. 2, 2004 deals with solar propulsion assist using reflection mode mini-optic twisting balls and twisting cylinders.
U.S. Pat. No. 6,957,894 issued to Mario Rabinowitz on Oct. 25, 2005 deals with group alignment of reflection mode micro-optic twisting balls and twisting cylinders using induced electric dipoles.
U.S. Pat. No. 6,964,486 issued to Mario Rabinowitz on Nov. 15, 2005 deal with alignment of reflection mode solar concentrator micro-mirrors by augmentation induced electric dipoles with permanent electric dipoles.
U.S. Pat. No. 6,987,604 issued to Mario Rabinowitz and David Vincent Overhauser on Jan. 17, 2006 deals with manufacture of low friction rotatable arrays of reflection mode microoptic twisting balls and twisting cylinders.
U.S. Pat. No. 6,988,809 issued to Mario Rabinowitz on Jan. 24, 2006 deals with reflection mode solar concentration systems using micro-optic twisting balls and twisting cylinders.
U.S. Pat. No. 7,077,361 issued to Mario Rabinowitz on Jul. 18, 2006 deals with reflection mode micro-optics concentrator systems for solar power satellites.
U.S. Pat. No. 7,112,253 issued to Mario Rabinowitz on Sep. 26, 2006 deals with manufacturing reflection mode mini-balls for solar energy concentrators and related applications.
U.S. Pat. No. 7,130,102 issued to Mario Rabinowitz on Oct. 31, 2006 deals with reflection illumination and projection systems that use reflection mode mini-balls having metallic mirrors.
U.S. Pat. No. 7,133,183 issued to Mario Rabinowitz on Nov. 7, 2006 deals with reflection mode micro-optics solar concentrators based on mini-optic twisting balls and twisting cylinders that use metallic mirrors for reflection and electric and/or magnetic addressing.
There are also serious disadvantages and fundamental distinctions of kind associated with other patents that use twisting balls in display technology. These technologies are called by various names such as electronic-paper, e-paper, or gyricon. It appears that none of the prior art associated with display technology utilizes the twisting balls to optically concentrate, or focus, light as is done in this present invention. Furthermore, the prior art neither teaches nor anticipates the use of optical transmission mode twisting ball or cylinder technology in for solar energy conversion applications. The following is a representative sample from the large body of gyricon and gyricon-like patents used in display technology.
U.S. Pat. No. 5,717,515 issued to N. K. Sheridon on Feb. 10, 1998 deals with gyricon display technology.
U.S. Pat. No. 5,754,332 issued to J. M. Crowley on May 19, 1998 deals with gyricon two-colored twisting balls having reflectance comparable to white paper for monolayer gyricon displays.
U.S. Pat. No. 5,808,783 issued to J. M. Crowley on Sep. 15, 1998 deals with gyricon two-colored twisting balls having high reflectance properties for use as a white paper replacement.
U.S. Pat. No. 5,914,805 issued to J. M. Crowley on Jun. 22, 1999 deals with the use of two sets of gyricon two-colored twisting balls with enhanced reflectance properties.
U.S. Pat. No. 5,940,054 issued to Ellis D. Harris on Aug. 17, 1999 deals with the use of the friction induced electric charges (Triboelectric effect) on optical elements to the purpose of inducing motion of the optical elements.
U.S. Pat. No. 6,055,091 issued to N. K. Sheridon and J. M. Crowley on Apr. 25, 2000 and shows the use of gyricon two-color cylinders for electronic displays.
U.S. Pat. No. 6,072,621 issued to E. Kishi, T. Yagi, and T. Ikeda on Jun. 6, 2000 and shows how sets of different single-colored polarized twisting balls can be use in a display device.
U.S. Pat. No. 6,097,531 issued to N. K. Sheridon on Aug. 1, 2000 describes a method for constructing magnetized twisting balls or cylinders for gyricon displays.
U.S. Pat. No. 6,120,588 to J. M. Jacobson on Sep. 19, 2000 shows an electronically addressable single color display.
U.S. Pat. No. 6,174,153 issued to N. K. Sheridon on Jan. 16, 2001 describes an addressable gyricon display.
U.S. Pat. No. 6,192,890 B1 issued to D. H. Levy and J. P. F. Cherry on Feb. 27, 2001 describes a reconfigurable display sign using magnetic and electric fields to reorient the particles in the display.
There are also serious disadvantages in the prior art of electrostatic motors. The prior art is either too complex, or does not have sufficient resolution for high-performance concentration.
U.S. Pat. No. 4,754,185 issued to Kaigham J. Gabriel, Robert K. Prud'Homme and William S. N. Trimmer on Jun. 28, 1988 describes an electrostatic actuator having electrodes on both the stator and rotor.
U.S. Pat. No. 5,585,683 issued to Toshiro Higuchi, Saku Egawa, Massao Hiyane, and Katsuhide Natori on Dec. 17, 1996 describes an electrostatic actuator having a plurality of belt-like electrodes positioned only on the stator or only on the rotor, which are driven with three or more voltage pulsed phases, wherein at least one of the phases is needed for avoiding an unpredictable bi-stable state found in systems composed of only two voltage driving phases. This meta-stable state causes the direction of travel of any of the actuators described therein to be indeterminant without at least a third set of electrodes, having a direction discriminating voltage. These direction discriminating electrodes are periodic and are intermingled with the other belt-like electrodes. The phases and function of each set of electrodes permutating with each discrete step of said electrostatic stepping motor. This prior art neither teaches or anticipates any techniques to avoid the meta-stable state by using other techniques other than one or more sets of periodic belt-like electrodes intermingled the other electrodes. This problem is directly addressed in the current invention in the context of a movable transmission mode optical device for solar tracking.
U.S. Pat. No. 5,869,916 issued to Hidetoshi Suzuki and Takeshi Tanaka on Feb. 9, 1999 describes an electrostatic actuator having electrodes on both the stator and rotor.
U.S. Pat. No. 5,965,968 issued to Phillippe Robert, Jean-Sebastien Danel, and Bernard Diem on Oct. 12, 1999 describes an electrostatic actuator driven by deformation waves induced by electric fields.
U.S. Pat. No. 6,657,359 issued to Storrs Hoen and Carl Taussig on Dec. 2, 2003 describes an electrostatic actuator having electrodes on both the stator and rotor.
In summary, there are a large number of prior art devices that are currently using a twisting ball or cylinder geometry for either display technology or for reflection mode solar concentration. However, none of these teaches or anticipates the present invention of transmission mode solar tracking and transmission mode concentration. Additionally, there are a large number of prior art electrostatic actuation devices but most of these are based on electrodes on both the stator and the rotor; additional deficiencies of the prior art include complexity due to a need to suppress a bi-stable state that makes direction of motor displacement impossible to determine without a means to force a predetermined direction of motion. Thus the prior art described above is seen to have multiple deficiencies. These deficiencies are addressed and overcome in this patent.